Off-wall electrode device and methods for nerve modulation

ABSTRACT

Medical devices and methods for making and using the same are disclosed. An example medical device may include an ablative catheter for nerve modulation through a wall of a blood vessel. The catheter may include a catheter sheath having a proximal end, a distal end, and a lumen extending from the proximal to the distal end. An elongate member may extend along a central elongate axis within the lumen of the catheter sheath. The elongate member having a proximal end and a distal end. An expandable ablative member may be coupled to the distal end of the elongate member having an insulative section connected to a bare electrode section. The ablative member may be configured to switch between a collapsed position and an expanded position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/581,430, filed Dec. 29, 2011, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to devices and methods for intravascular neuromodulation. More particularly, the technologies disclosed herein relate to apparatus, systems, and methods for achieving intravascular renal neuromodulation via thermal heating.

BACKGROUND

Certain treatments require temporary or permanent interruption or modification of select nerve functions. One example treatment is renal nerve ablation, which is sometimes used to treat conditions related to hypertension and congestive heart failure. The kidneys produce a sympathetic response to congestive heart failure, which among other effects, increases the undesired retention of water and/or sodium. Ablating some nerves running to the kidneys may reduce or eliminate this sympathetic function, providing a corresponding reduction in the associated undesired symptoms.

Many nerves, including renal nerves, run along the walls of or in close proximity to blood vessels, and these nerves can be accessed via the blood vessel walls. In some instances, it may be desirable to ablate perivascular renal nerves using a radio frequency (RF) electrode. Such treatment, however, may have an increased risk of thermal injury to the vessel at the electrode and other undesirable side effects such as, but not limited to, tissue damage, clotting, and/or protein fouling of the electrode. To prevent such undesirable side effects, some techniques attempt to increase the distance between the vessel walls and the electrode.

Therefore, there remains room for improvement and/or alternatives in providing systems and methods for intravascular nerve modulation.

SUMMARY

The disclosure is directed to several alternative designs, materials, and methods of manufacturing medical device structures and assemblies.

Accordingly, some embodiments pertain to an ablative catheter system for nerve modulation through the wall of a blood vessel, including a catheter sheath extending along a central elongate axis and having a proximal end, a distal end, and a lumen extending from the proximal to the distal end. The catheter system further includes an elongate member with a proximal end and a distal end, and an expandable ablative member coupled to the distal end of the elongate member. The ablative member may include an insulating section and a bare electrode section. Further, the ablative member is configured such that it may be moved between a collapsed position and an expanded position. In the expanded position, a portion of the insulative section contacts the walls of the vessel lumen and the bare electrode section is at a distance from the vessel lumen wall. The ablative member may be self-expanding or may be expanded by an actuating means such as a balloon or by push-pull actuation. Further, the ablative member may be one or more spiral coils formed as an hourglass. Alternatively, the ablative member may be formed of conductor wires expandable to form two or more humps and one or more troughs in between. The bare electrode sections may be positioned in the troughs and the insulative sections may be positioned in the humps.

Some embodiments pertain to a renal ablation system for nerve modulation through the wall of a blood vessel, including an elongate member extending along a central elongate axis. The elongate member has a proximal end and a distal end. The system further includes a self-expandable ablative member coupled to the distal end of the elongate member. The ablative member may have one or more conductor wires, which include one or more bare electrode sections. The electrode sections have a proximal and distal end and these electrode sections may be positioned at approximately at the center of the ablative member. The conductor wires may further include one or more insulative sections coupled to one or both of the proximal and the distal end of the bare electrode sections. The ablative member is configured to switch between a collapsed position and an expanded position, such that in the expanded position, the insulative portions contact the wall of the blood vessel and the bare electrode sections are positioned at a distance from the wall of the blood vessel.

Some embodiments also pertain to a method for ablating a nerve perivascularly through a vessel lumen. The method includes advancing a nerve modulation catheter such as an ablative catheter intravascularly proximate a desired location in a vessel lumen. In some embodiments, the ablative catheter includes a catheter sheath and an expandable ablative member having one or more bare electrode sections approximately at the center of the ablative coil and one or more insulative sections extending from the proximal end and distal end of the bare electrode sections. The method further deploys the expandable ablative coil in an expanded position in the vessel lumen such that portions of the insulative sections contact the walls of the vessel lumen and the bare electrode sections maintain a distance from the walls of the vessel lumen. Next, the bare electrode sections are activated to ablate at least a portion of the renal nerve without injuring the vessel walls.

The summary of some example embodiments in not intended to describe each disclosed embodiment or every implementation of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating a renal nerve modulation system in situ.

FIG. 2A is a schematic side view of the distal portion of an example ablative catheter system with an ablative member in the expanded state.

FIG. 2B illustrates the distal portion of the ablative member of FIG. 2A in a collapsed position.

FIG. 2C is a cut away sectional view of the ablative member of FIG. 2A taken along line A-A′.

FIG. 3 illustrates a side view of the distal end of an example ablative catheter system in an expanded position within a blood vessel.

FIG. 4 illustrates another side view of an example ablative catheter system according to some embodiments of the present disclosure.

FIGS. 5A-5B illustrate a side view of various example multi-filament ablative members.

FIGS. 6A-6B illustrate a side view of various example configurations of the ablative member.

FIG. 7A illustrates another side view of an example embodiment of the ablative member in a compressed state.

FIG. 7B illustrates the ablative member of FIG. 7A in an expanded position.

FIG. 8 illustrates a side view of an example two-wire ablative member in the expanded position.

FIG. 9 illustrates a side view of an example multi-wire ablative member in the expanded position.

While embodiments of the present disclosure are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular embodiments described. One the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in the specification.

All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the term “about” may be indicative as including numbers that are rounded to the nearest significant Figure.

The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

Although some suitable dimension ranges and/or values pertaining to various components, features, and/or specifications are disclosed, one of skill in the art, incited by the present disclosure, would understand desired dimensions, ranges and/or values many deviate from those expressly disclosed.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The detailed description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure. The illustrative embodiments depicted are intended only as exemplary. Selected features of any illustrative embodiment may be incorporated into an additional embodiment unless clearly stated to the contrary.

While the devices and methods described herein are discussed relative to renal nerve modulation, it is contemplated that the devices and methods may be used in other applications where nerve modulation and/or tissue ablation are desired. In addition to nerve modulation, the present apparatus and methods can be applied to modulation or ablation of other tissues in the body.

In some instances, it may be desirable to ablate perivascular renal nerves with deep target tissue heating. However, as energy passes from an electrode to the desired treatment region, the energy may heat the fluid (e.g. blood) and tissue as it passes. As more energy is used, higher temperatures in the desired treatment region may be achieved, but may result in some negative side effects, such as, but not limited to, thermal injury to the vessel wall, blood damage, clotting, and/or electrode fouling past the electrode and the vessel wall. Positioning the electrode away from the vessel wall may provide some degree of passive cooling by allowing blood to flow past the electrode.

FIG. 1 is a schematic view of an illustrative renal nerve modulation system 100 in situ. System 100 may include one or more conductors 102 for providing power to an ablative member 104 disposed within a catheter sheath or guide catheter 106, the details of which can be better seen in subsequent figures. A proximal end of the conductor 102 may be connected to a control and power element 108, which supplies the necessary electrical energy to activate the one or more electrodes (not shown) at or near a distal end of the ablative member 104. In some instances, return electrode patches 110 may be supplied at a convenient location on the patient's body to complete the circuit. The control and power element 108 may include monitoring elements to monitor parameters such as power, temperature, voltage, impedance, pulse size and/or shape and other suitable parameters as well as suitable controls for performing the desired procedure. In some instances, the power element 108 may control a radio frequency (RF) electrode. The electrode may be configured to operate at a frequency of approximately 460 kHz. It is contemplated that any desired frequency in the RF range may be used, for example, from 100-500 kHz. However, it is contemplated that different types of energy outside the RF spectrum may be used as desired, for example, but not limited to ultrasound, microwave, and laser.

FIGS. 2A and 2B are schematics of an exemplary ablative catheter system 200 according to embodiments of the present disclosure. More particularly, FIG. 2A is a side view of the catheter system 200 in an expanded state, while FIG. 2B is a side view of the catheter system 200 in a collapsed or compressed state. The ablative catheter system 200 includes catheter sheath 106 having a distal end 206, an elongate member 208 within the sheath lumen and having a distal end 212, and an expandable nerve modulation member, such as the ablative member 104 coupled to the elongate member's distal end 212. The ablative member 104 has a distal end 214. The catheter system 200 may further include proximal elements such as those shown in FIG. 1.

The sheath 106 may be substantially circular and it may be made of any suitable biocompatible material such as polyurethane, polyamide, polyether block amide (PEBA), silicones, fluoropolymer, PVC, metal or fiber reinforced material, a composite material, or a layered material, or a construction of multiple materials. Other suitable cross-sectional shapes such as elliptical, oval, polygonal, or irregular are also contemplated. Moreover, the sheath 106 may have a uniform flexibility along its entire length or adapted for variable flexure along portions of its length. For example, the sheath's distal end 206 may be more flexible while the remaining sheath may be less flexible. Flexibility allows the sheath 106 to maneuver turns in the circuitous vasculature, while greater stiffness provides the necessary columnar strength to urge the sheath 106 forward. The diameter of the sheath 106 may vary according to the desired application, but it is generally smaller than the typical diameter of a patient's vasculature. Moreover, the diameter of the sheath 106 may depend on the diameter of the elongate member 208 and the ablative member 104.

In one embodiment, the elongate member 208 is a conductor covered by an insulative material. The proximal end of the conductor may be connected to a power source such as an external power generator or battery incorporated in the handle. The distal end of the conductor may be connected to the ablative member 104 or other operative member.

FIG. 2A illustrates the ablative member 104 in an expanded state. In this state, some portions of the ablative member 104 contact the blood vessel walls and some portions remain at a distance from the walls. Electrodes 220 are positioned on the portions of the member 104 that remain at a distance from the wall. Depending on the desired application, electrodes 220 may be placed at various locations along the ablative member 104. For example, in one instance (not shown), the electrodes 220 may be placed slightly away from the wall. Alternatively, as shown in FIG. 2A, the electrodes 220 may be placed such that they are centered in the vessel.

Moreover, the ablative member 104 may be formed of a conductor 222 with an insulative layer 224. FIG. 2C is a sectional view of the ablative member 104 taken along line A-A′ in FIG. 2A, showing the conductor 222 and the layer 224. Portions of the ablative member 104 that contact the vessel surfaces include the layer 224, and portions where electrodes 220 are present are bare. For example, the center portion of the ablative member 104 may be without a layer 224, while all other portions may have the insulative layer 224. When electrical signals are passed through the conductor 222, the bare portions act as electrodes 220. Therefore, based on the required number and position of electrodes 220, portions of the ablative member 104 are left bare.

FIG. 2B is a schematic illustrating the distal portion of the ablative catheter system 100 with the ablative member 104 in the compressed state. From this state, the ablative member may be expanded using various actuating means, depending on the properties of the ablative member. For instance, the ablative member 104 may be self-expandable or expanded by application of a force. Self-expandable members may be formed of any material that can expand to its expanded configuration when released from a sheath. Such members may be formed of elastic materials such as stainless steel, shape memory alloys such as Nitinol or any other suitable material commonly known in the art.

According to another technique, pull wires (not shown) may be utilized. Pull wires may be attached to the member's distal end 214, for example. When the pull wire is pulled proximally, it places a tensile force on the ablative member 104, compressing it longitudinally to its radially expanded state. When the pull wire is released, the tensile force is released permitting the ablative member 104 to elongate to its radially collapsed state.

In case of ablative members 104 that are expanded by some external force, the member 104 does not expand on its own and an expansion means may be required to place an outward radial force on the member 104 to expand it. Such expansion means (not shown) may include balloons or dilators. Other such expansion means may also be utilized without departing from the scope of the present disclosure. For example, means such as springs, or levers may be utilized to expand the ablative member 104. Similarly, the ablative member 104, itself, may be formed of pivotal structures connected to one another. For instance, the member may be formed of multiple wires connected to one another along pivotal joints. An outward force on the pivotal point expands the various wires connected to the point, expanding the ablative member 104.

The expansion of the ablative member should be such that it does not cause damage to the artery by exerting a large force on the vessel walls. To prevent such large expansion force, the ablative member may include visualization devices such as cameras, fluorescent dyes, radiopaque markers or other visualization aids to visualize the extent of expansion. Further, the ablative member may include a force or expansion-limiting component that prevents the member from expanding beyond a certain limit. Often, the expansion limit may be set during manufacturing of the ablative member. For example, operators may know the average size of renal arteries, and they may ensure the ablative member does not expand beyond the average artery size. For example, the diameter of the expanded member may be maintained below about 4 mm, 6 mm, 8 mm or other desired size.

FIGS. 2A-2C illustrate a general ablative catheter system and ablative member 104 according to embodiments of the present disclosure. The following Figures and description illustrate specific exemplary configurations of the ablative member 104.

FIG. 3 is a schematic illustrating a distal portion of the ablative catheter system 200 within a blood vessel 301 in a patient's body. Here, the ablative member 104 is in the expanded state. The ablation member spirals into a helical, hourglass shape, generally indicated as hourglass shape 302. Further, the ablative member 104 may be formed as a spiral electrode coil having a proximal portion 303, a distal portion 304, and a central portion 306. The proximal and distal portions are covered with an insulative material, and a portion of the central portion 306 is bare, forming electrode 220.

As illustrated, the distal and proximal portions expand the most, deviating to such a degree from the centre of the vessel that they contact the wall of the blood vessel. The central portion 306, on the other hand, expands less (or not all all), deviating from the central longitudinal axis such that a gap is formed between the wall of the blood vessel 301 and the electrode 220.

The hourglass shape 302 is formed with the proximal and distal ends forming the two glasses and the central portion 306 forming the stem between the glasses. This shape, eliminates the chance of the electrode 220 touching the artery walls and causing wall injury. Further, being centered in the artery, the electrode 220 may circumferentially radiate RF energy equally ablating the nerves surrounding the artery.

The curvature of the central portion 306 may be controlled by the heat set geometry of the coil. For example, a small amount of narrowing may be used to position the electrode 220 about 0.5 mm from the artery wall. Alternatively, more narrowing may be incorporated to position the wire close to the center of the artery. In some embodiments, the electrode 220 may be arranged at any place along the spiral except the portions contacting the wall of the blood vessel 301. For example, to ablate nerve tissues closer to one side of the vessel wall, the electrode 220 may be placed anywhere between the central portion 306 and the proximal or distal portions.

The rigidity and characteristics of the material used to form the ablative member 104 determine the member's expandability. For example, the thickness of the material may vary between the central portion 306, and the distal and proximal portions, causing the central portion 306 to deviate slightly and the proximal and distal portions to deviate more. Similarly, the material composition may vary between the central and end portions varying the expandability of these portions. For example, materials such as, but not limited to, stainless steel or nitinol may be used to form one portion, while tungsten, platinum, palladium, other metals or a suitable polymer may be used to form other portions. Other techniques to vary the expandability of the coil may be employed just as easily such as varying the heat treatment of the thermal “set” of the material along the length, varying the material dimensions, varying coatings or coverings, etc.

FIG. 4 illustrates the distal portion of an exemplary ablative catheter system 400 in the blood vessel 301. This example is similar to FIG. 3 except the central portion 306 is straightened such that the electrode 220 is arranged to be a straight segment along the center of the artery. This configuration, thus, applies equal circumferential RF ablation along the length of electrode 220.

FIGS. 5A and 5B illustrate the distal portion of another exemplary ablative catheter system 500. Here, the ablative member 104 includes multiple self-expandable coils or filaments 502. The coils may all expand in the same direction as illustrated in FIG. 5A, or expand in different directions, as illustrated in FIG. 5B. Each coil may independently form an hourglass configuration or the complete multi-filament structure may also form the hourglass configuration. Further, the coils may be loosely braided with the bare electrode portions of each coil in the central portion 306.

Alternatively, the bare electrode portion for each coil may be at a different location along the coil, so that the electrodes 220 target different ablation sites. For example, the electrode 220 for one coil may be in the central portion 306, for another coil may be in the proximal portion 303, and for a third coil may be in the distal portion 304. Further, the degree of expansion, the materials used, and the thickness of the coils may vary within the coils without departing from the scope of the present disclosure. Moreover, different levels of narrowing may be carried out for the different coils so that the electrodes 220 are at a varied distance from the artery walls.

Using multiple filaments 502, more electrodes 220, or electrodes having larger surface area, may be created in the central portion 306, which can together deliver more energy than a single electrode 220 without blood coagulation or electrode fouling, and therefore ablate a given nerve more quickly and efficiently. Increased energy delivery, however, may raise the temperature around the coil considerably and, therefore, blood with greater velocity may be required to cool the area sufficiently. A number of cooling techniques are known in the art and any of these cooling techniques may be utilized to cool the vessel without departing from the scope of the present disclosure.

The multi-strand braid of FIG. 5 may be formed of metal, polymer, or a combination of the two. For example, the polymer filaments may provide centering and position control, while the metal may be used as the electrode 220. In one embodiment, the filaments 502 may have a metal core and a polymer outer covering over the insulative portions. Further, any suitable biocompatible metal or polymer may be utilized to form the filaments 502. Exemplary metals may include, but not limited to, platinum, gold, stainless steel, steel, cobalt alloys, nitinol, or other such non-oxidizing materials. In some instances, titanium, tantalum, or tungsten may be used. Exemplary polymers include polyurethane, polyamide, polyether block amide (PEBA), silicones, fluoropolymer, PVC, a composite material, a layered material, or a construction of multiple materials.

The embodiments illustrated in FIGS. 2-5 illustrate a self-expandable member formed into an hourglass shaped coil. FIGS. 6A and 6B illustrate a few alternate embodiments where the coil may take different shapes. For example, FIG. 6A illustrates an ablative member 104 in the form of a decreasing spiral 602. The proximal end of the member 104 may expand the most, contacting the wall of the blood vessel 301, and the distal end of the member 104 may not expand at all. The ablative member 104 thus forms an inverted V shaped member. The electrode 220 may be placed at the distal end of the member 104, or at any other positions along the coil that do not contact the walls of the artery. In case the electrode 220 is placed at the distal end, it may be placed at a little distance from the distal end of the member 104. This insulative portion 224 at the distal tip ensures that even if the distal end contacts the vessel walls inadvertently, the electrode does not contact the wall.

FIG. 6B illustrates the ablative member in the form of an increasing spiral 604 where the proximal end of the ablative member 104 expands the least and the distal end expands the most. Here, the distal end contacts the vessel walls, while the central and proximal portions do not. Electrodes 220 may be placed anywhere along the central or proximal portions of the ablative member 104 without departing from the scope of the present disclosure. Further, two or more electrode 220 may also be placed at different locations along the ablative member 104 to ablate different nerve sites without moving the catheter system 200.

It will be understood that other variations in configuration are possible as long as the ablative member 104 includes insulative portions in contact with the vessel walls and bare electrode portions away from the vessel walls. For example, the ablative member 104 may be made of expandable conductor wires shaped as an ellipse or a circle. The elliptical or circular member may be stored in a compressed state within the sheath 106, and when the member 104 is actuated to extend beyond the distal end 206 of the sheath 106, the member 104 may expand. In this type of member 104, the electrodes 220 may be positioned at the distalmost or proximal end of the member 104. Alternatively, the ablative member 104 may have a zigzag shape, bends, or bumps to position the electrodes 220 as desired.

FIGS. 7A and 7B illustrate yet another exemplary ablative member 104. More particularly, FIG. 7A illustrates the ablative member 104 in the compressed state and FIG. 7B illustrates the ablative member 104 in the expanded or deployed state. In the compressed state, the ablative member 104 remains straight within the blood vessel 301. In case the ablative member 104 is self-expandable, any known technique may be utilized to keep the ablative member 104 compressed, such as by compression within the sheath 106 or by using pull wires. In case the ablative member 104 requires external force, the external force is not applied in the compressed state.

In case of ablative member 104, for expansion, the member 104 may be extended beyond the sheath 106, or the pull wires may be released. Alternatively, external forces, such as a balloon, a dilator, or other such means may be utilized to expand the member 104. In the expanded state, the proximal and distal portions of ablative member 104 remain along the longitudinal axis while a central portion expands to form two humps 702. A trough 704 is formed between the two humps 702 and this trough 704 is the bare portion of the ablative member forming the electrode 220.

As described previously, the degree of expandability of the humps 702 and their degree of inclination may depend on a number of factors such as material used, thickness of the material, desired geometry, etc. For example, the bare electrode portion may be narrowed such that it dips away from the artery walls. In other embodiments, the wire may have three or more humps 702, allowing for the placement of multiple electrodes 220 on the same wire. Moreover, the distance of the trough 704 from the peak of the humps 702 may vary allowing operators to place electrodes 220 at different distances from the artery walls, and therefore adjusting the distribution of RF energy.

FIG. 8 illustrates another exemplary ablative member, which includes two electrode wires 802 expanding in opposite directions, and therefore centering the ablative member 104 with respect to the vessel 301. It will be understood that, instead of both the wires 802 having the same expandable configuration (as shown in FIG. 8), their configurations may vary. For example, one wire may include two humps 702 and the other wire may include three or no humps. No humps may be formed when the wire forms a simple bow structure. These wires 802 may be completely insulated and they may not include any electrodes.

It will be understood that, instead of two wires 802, multiple such electrode wires 802 may be incorporated in the ablative member 104. FIG. 9 illustrates such an embodiment. In some instances, each wire 802 may include at least one portion contacting the blood vessel wall, and at least some wires 802 may include a bare electrode region. As illustrated in this Figure, only one wire includes an electrode 220, while the other wires 802 are merely included for centering and positioning the ablative member 104. In some instances, the bare electrode region of all the wires may be equidistant from the vessel walls. Alternatively, the electrodes 220 may be placed at different distances from the wall of the blood vessel 301. Some electrodes 220 may be closer to the artery walls than others. Moreover, the electrodes 220 may not be placed in the trough 704 between the humps 702. Instead, they may be placed on any other portions of the wires 802 not contacting the vessel surface. For example, the electrodes 220 may be placed towards the distal or proximal ends of the ablative member 104.

The ablative members 104 illustrated in FIGS. 2-9 have a configuration that allows blood to flow through the expandable material for cooling the structure and the artery wall. Even the multi-filament structures are loosely braided structures that allow blood to flow through the member 104, cooling it. Because the structure does not block much of the artery during modulation, this structure minimizes blood stasis, reduces thrombosis, and provides renal perfusion.

Further, to monitor the temperature of the electrodes 220 and the blood vessel 301 walls, one or more sensors, such as temperature sensors, may be placed at different portions of the ablative member 104. For instance, one sensor may be placed near the electrode 220 to monitor electrode fouling or electrode temperature and another sensor may be placed in the portion contacting the vessel wall to measure the temperature at the blood vessel. External devices connected to the sensors may be configured to raise alerts if any of the sensors detect temperatures over a preconfigured threshold value. If an alert is raised, operators may discontinue modulation until the temperature at the electrode or at the vessel wall returns under the threshold value. Alternatively, operators may simply monitor the temperatures and discontinue when they feel temperatures exceed a certain value.

The insulative covering on the ablative member 104 provide electrical isolation but still may conduct heat. This heat conductive property allows operators to place temperature sensors such as thermocouples on the insulative portions to measure temperature.

The ablative catheter system 200 may be operated in various modes. In unipolar ablation, a distant ground pad or electrode is typically used to complete the circuit. In one embodiment, the system 200 may be operated in a sequential unipolar ablation mode. In this mode, the electrodes may each be connected to an independent power supply such that each electrode may be operated separately. In sequential unipolar ablation, one electrode may be activated at a time. The next electrode is activated only after a first electrode is activated and deactivated.

In another instance, the system 200 may operate in a simultaneous unipolar mode. In this mode, the electrodes may be activated simultaneously. In some embodiments, the electrodes may each be connected to independent electrical supplies. Independent power supplies provide more control of the ablation energy supplied to each electrode. Alternatively, the electrodes may all be connected in parallel to the same electric supply. In this mode, more current may be dispersed radially as all the electrodes collectively emanate current at the same time. This dispersion may result in a more effective, deeper penetration compared to the sequential unipolar mode.

In another embodiment, a bipolar ablation mode may also be employed. In this mode, two electrodes disposed at the treatment location may be used to complete the circuit without a distant ground pad or electrode such that current may flow around the ablative member from one electrode to the other. In general, either sequential or simultaneous unipolar mode may penetrate more deeply than the bipolar mode. Any of the embodiments described in this disclosure may be operated in any of the above-described modes.

In use, the system 200 may be introduced percutaneously as is conventional in the intravascular medicinal device arts. For example, a guidewire may be introduced percutaneously through a femoral artery and navigated to a renal artery using standard radiographic techniques. The catheter sheath 106 may be introduced over the guide wire and the guide wire may be withdrawn. The elongate member and the ablative member may then be introduced in the catheter sheath 106 and urged distally to the desired location. Once there, the sheath may be retracted proximally to allow the ablative member to expand or the ablative member may be urged distally to extend beyond the distal end of the sheath.

The electrodes may then be activated to ablate nerve tissue. During this procedure, the ablative member may continuously monitor the temperature at the electrodes and the vessel walls. Further, the electrodes may be activated sequentially or simultaneously, as desired. Known monitoring techniques may be utilized to monitor the tissue being ablated. Once the tissue is sufficiently ablated, the catheter sheath may be advanced or the ablative member may be retracted to compress the ablative member and retrieve it from the patient's body.

Those skilled in the art will recognize that the present disclosure may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departure in form a and detail may be made without departing from the scope and spirit of the present disclosure as described in the appended claims. 

What is claimed is:
 1. An ablative catheter for nerve modulation through a wall of a blood vessel, the catheter comprising: a catheter sheath having a proximal end, a distal end, and a lumen extending from the proximal to the distal end; an elongate member extending along a central elongate axis within the lumen of the catheter sheath, the elongate member having a proximal end and a distal end; an expandable ablative member coupled to the distal end of the elongate member having an insulative section connected to a bare electrode section; and wherein the ablative member is configured to switch between a collapsed position and an expanded position extending out of the distal end of the catheter sheath such that a portion of the insulative section contacts the wall of the blood vessel and the bare electrode section is disposed at a distance from the wall of the blood vessel, the expandable ablative member having a generally helical shape of variable outer diameter.
 2. The ablative catheter of claim 1, wherein the ablative member is self-expandable.
 3. The ablative catheter of claim 1, wherein the ablative member is expanded by an actuating means.
 4. The ablative catheter of claim 1, wherein the ablative member is a spiral coil configured in an hourglass shape having a first end, a second end and a waist therebetween.
 5. The ablative catheter of claim 4, wherein the insulative sections form the two ends of the hourglass shape and the bare electrode section forms a waist of the hourglass shape.
 6. The ablative catheter of claim 4, wherein the ablative member includes a plurality of spiral coils loosely braided.
 7. The ablative catheter of claim 1, wherein the ablative member is an expandable wire configured to form two or more humps and one or more troughs in between the two or more humps in the expanded position such that the insulative sections form the two or more humps and the bare electrode section form the one or more troughs.
 8. The ablative catheter of claim 7, wherein the ablative member includes a plurality of expandable wires.
 9. The ablative catheter of claim 1, wherein, in the expanded position, an outer diameter of the ablative member increases distally.
 10. The ablative catheter of claim 1, further comprising one or more temperature sensors coupled to the portion of the insulative section in contact with the wall of the blood vessel in the expanded position.
 11. A renal ablation system for nerve modulation through a wall of a blood vessel, the system comprising: an elongate member extending along a central elongate axis, the elongate member having a proximal end and a distal end; an expandable ablative member coupled to the distal end of the elongate member, the ablative member having one or more conductor wires, the conductor wires comprising: one or more bare electrode sections each having a proximal end and a distal end, and one or more insulative sections; the ablative member configured to switch between a collapsed position an expanded position; and wherein in the expanded position, the insulative portions contact the wall of the blood vessel and the bare electrode sections are positioned at a distance from the wall of the blood vessel.
 12. The renal ablation system of claim 11, wherein the conductor wires are spiral coils.
 13. The renal ablation system of claim 12, wherein, in the expanded position, the spiral coils forms an hourglass shape.
 14. The renal ablation system of claim 12, wherein the ablative member includes multiple spiral coils loosely braided to form an hourglass shape.
 15. The renal ablation system of claim 11, wherein, in the expanded position, one or more of the conductor wires are configured to form two or more humps and one or more troughs, such that the insulative sections form the two or more humps and the bare electrode sections form the one or more troughs.
 16. The renal ablation system of claim 11, wherein the expandable ablative member is biased to the expanded position.
 17. The renal ablation system of claim 11, wherein the expandable ablative member includes at least one insulative section proximal the bare electrode sections and at least one insulative section distal the bare electrode sections.
 18. A method for ablating tissue through a vessel lumen, the method comprising: advancing an ablative catheter intravascularly proximate a desired location in a blood vessel, the ablative catheter including an elongate member and an expandable ablative member having one or more bare electrode sections disposed along a center region of the ablative member and one or more insulative sections extending from the proximal end and distal end of the bare electrode sections; deploying the expandable ablative member in an expanded position in the vessel lumen such that portions of the insulative sections contact a wall of the blood vessel and the bare electrode sections maintain a distance from the wall of the blood vessel; and activating the bare electrode sections to ablate at least a portion of a target tissue.
 19. The method of claim 18, wherein the target tissue is perivascular nerve tissue.
 20. The method of claim 18, wherein the expandable ablative member includes a plurality of generally helical elongate members, each of the plurality of generally helical elongate members comprising a bare electrode section and an insulative section. 